This project covers the design, synthesis and use of new reagents and chemical constructs that will meet specific requirements in research projects of collaborating groups or individuals. Research goals fall within the fields of basic and applied immunology and structural biology. For the preparation of conjugates and immunoadsorbents, heteroligation strategies have played a central role our work. In these strategies, two disparate structures are cross-linked without self-polymerization by placing uniquely interacting functions on each component through chemical derivatization. We have favored the use of sulfhydryl and sulfhydryl- selective groups as the paired functions, with cross-linking occurring through formation of stable thioether linkages. New reagents have been developed for the placement of sulfhydryl- selective, haloacetyl (chloro-, bromo- and iodoacetyl) groups onto proteins, peptides and polymers. In particular, we have introduced a reagent ("BBAL") for placing a bromoacetyl moiety at any desired sequence position of a synthetic peptide, so that the resulting peptide may be directly coupled to sulfhydryl-bearing carriers at this designated position. Peptides that are synthesized with both bromoacetyl- and sulfhydryl-bearing (cysteinyl) residues may be self-polymerized to produce immunogens, or cyclized under different conditions to yield conformationally constrained epitopes for grafting onto immunogenic carriers. We have designed and used improved iodoacetylating agents and also reagents for placing protected/activated sulfhydryl groups on oxidized polysaccharide chains of antibodies and other glycoproteins. The terminal sulfhydryl group is spaced from the polysaccharide chain by intervening structures in order reduce steric hindrance to the approach of macromolecular reactants. We have recently designed, synthesized and tested a selective alkylating agent for cysteine side chains in proteins that permits positive identification of Cys residues as a phenylthiohydantoin (PTH) analogue in the course of microsequencing of amino acids in peptide fragments (at less than or equal to 10 pmole level). The polarity of the new, stable PTH derivative, resulting from the Edman degradation through Cys positions, is such that its HPLC peak falls in an unused portion of the standard chromatogram. This finding solves the major remaining analytical problem in the chemical structure determination of peptides/proteins at the ultramicro level.